.fill([]) | New Array
+----------+------+------+------+------+
| | | | | |
Memory | [] |indx0 |indx1 |indx2 |indx3 |
| | | | | |
+----------+------+------+------+------+
^ | | | |
| | | | |
+--------+ | | |
+---------------+ | |
+----------------------+ |
+-----------------------------+
The four indexes are pointing to the same value in memory, so when you're pushing an element, you're doing on the same value (array) in memory.
